Abnormal penetration of exogeneous norepinephrine (NE) through the BBB was evaluated in cerebral ischemia produced in gerbils by unilateral occlusion of the common carotid artery. The preliminary findings indicate that the peak of such penetration occurs 72 hours after release of 1 hour occlusion. This was demonstrated by quantitative assay using 3H labeled tracer and by radioautography. Extravasation of exogeneous NE into brain parenchyma induced also a formation of bizarre noradrenergic structures in the vicinity of ischemic lesions.